This invention relates generally to cargo containers, and in particular, to a transparent cargo container offering the ability to visually inspect the contents without opening the container.
Since the dawn of the industrial age, manufacturers, distributors and shippers have strived to develop efficient and cost effective ways to transport goods. Sailing ships, horse and ox drawn carts gave way to ocean freighters, trains, trucks and eventually, the airplane.
Where transported goods were once stowed individually within the transport vehicle, today, the goods are often prepackaged within containers prior to transport. Such containers include, but are not limited to, intermodal transport carriers, semi-trailers and air cargo containers.
Products for inter-country shipment are usually loaded into an intermodal freight container at a site of manufacturer and shipped to a seaport by rail transportation. The intermodal freight container is then loaded into an ocean-going ship for transport between continents. Upon arrival at the destination continent, the intermodal freight container is removed from the ship and loaded onto a railroad transport car for delivery to a particular city where the container can be loaded onto a truck transport for delivery to a local destination.
The modern semi-trailer is removable from its tractor unit (used for hauling), generally attached by a xe2x80x9cfifth wheelxe2x80x9d. More recently, a second truck trailer may be removably attached to the first truck trailer.
The modern air cargo container is a monocoque structure comprising a rigid frame to which a sheet material, generally referred to as the xe2x80x9cskinxe2x80x9d is attached to the frame. The ideal air cargo container is light in weight, low in cost and capable of withstanding both inflight stresses and the day to day rigors of service without being damaged.
In the past, the side walls of containers and container structures have generally been manufactured from opaque materials, such as aluminum, sheet metal and fiberglass. Side panels used to form the side walls have been attached to the container frame most often using a bolt or rivet that passed through the panel. Transparent side panels have been attempted in the past to aid cargo handlers in determining how or to what extent the cargo container has been loaded. Transparent side panels have also been contemplated to help discourage undesired acts of pilferage.
As governmental authorities have become more concerned with terrorist and other security threats, a higher percentage of sealed opaque containers are being opened for visual inspection, adding both delay and increased cost to shipping. Transparent side panels have the ability to allow easy and efficient visual access to security personnel to assist them in determining whether the container contents have been altered since their original loading or pose some other security risk.
Polycarbonate sheet material has often been considered for use as transparent container side walls. It is transparent, can be struck heavily without being dented, torn or broken, it is light in weight, and is only slightly more costly than the aluminum alloys currently in use.
However, polycarbonate sheet material also has some distinct disadvantages for use as a container side wall material. It has a very high coefficient of thermal expansion, 0.000037 inches per inch per degree Fahrenheit, compared to 0.000013 for aluminum or 0.0000063 for steel. Conventional wisdom has held that for containers encountering wide ranges in temperature variation, mounting holes would have to be oversize in diameter or slotted on each side of the panel. The resultant looseness or xe2x80x9cslopxe2x80x9d of the panel would reduce the load bearing capability of the panel, requiring heavier and more costly supporting frames.
Polycarbonate sheet material also has the disadvantage of being susceptible to stress induced and crazing agent induced cracking or crazing. When residual stresses remain in polycarbonate, the material is subject to cracking, particularly in the presence of crazing agents, such as hydrocarbons and jet fuel cleaning materials. Once cracked, the cracks spread very easily.
Prior attempts at utilizing plastic side wall materials have included the following:
U.S. Pat. No. 5,180,078 to Looker, directed to an air cargo container in which a polycarbonate sheet material is used as the skin of the structure. The attachment assembly includes a significant area of overlap between the polycarbonate and metal components as well as an attachment strip which substantially covers the attachment area. Rivets or bolts are inserted through oversized holes in the metal, polycarbonate, and attachment strip and then torqued, creating a rigid joint.
U.S. Pat. No. 5,178,292 to Korzeniowski is directed to an intermodal freight container constructed substantially of reinforced plastic composite material. The container includes a space frame structure which contains a reinforced plastic composite brace extending between and secured to the roof and sidewall, forming a somewhat tri-angularly shaped main upper composite frame beam in the container.
U.S. Pat. No. 4,936,477 to King et al. is directed to a cargo container which includes a number of elongated frame members each having an elongated channel and an elongated recess, and a number of coupling members removably engageable with the ends of the frame members. A number of panels are removably engageable within the elongated channels in the frame members. Each of the panels has an elongated recess around a perimeter which, together with the elongated recess in each of the frame members, forms an elongated slot. A locking element is removably insertable into the slots formed by the panel recesses and the frame member recesses when the panels are in engagement with the channels, to lock the frame members, panels and coupling members into a substantially rigid assembly. The panel is glued around its perimeter to a rigid perimeter edge.
U.S. Pat. No. 6,161,714 to Matsuura et al. is directed to a cargo container where the sidewalls are made of fiber reinforced plastic plates. Other parts of the container, such as the frame and door are made of any conventional metallic material. The mount portions containing the holes for the rivets or bolts are made thicker than other portions of the container.
U.S. Pat. No. Re. 34,892 to Dunwoodie is directed to a container using interlocking corner joints. At least one nut and bolt combination is inserted through aligned holes in an outer and inner corner molding strips and tightened to compress and retain the outer and inner corner molding strips to an outer side skin inserted between them in a releasable lengthwise relation. An inner side skin forms an interior wall of the container in similar fashion.
U.S. Pat. No. 5,255,806 to Korzeniowski et al. is directed to a reinforced plastic composite intermodal vehicle hauler. Aligned and interconnected panels which include integrally formed ribs form the sidewalls. The walls are made of a reinforced plastic composite material.
In the previous attempts at creating plastic sidewalls, significant effort is required to replace a damaged side panel. Removal of the panel requires disassembly of numerous nut and bolt combinations, or shearing of numerous rivets, often requiring special tools.
Accordingly, there remains a continuing need for improved methods to attach clear polycarbonate and other sheet material to a structural element to be used as a transparent side panel for a shipping container. The present invention fulfills this need, and further provides related advantages.
The novel attachment of a polycarbonate or other plastic sheet material to a structural frame described by this invention allows for non-slip placement of the side wall, easy and economical replacement of a damaged side wall, and does not induce cracking or crazing of the plastic sheet material.
A structural frame is channeled to receive an edge of the sheet material. Contained within the channel is a weather resistant deformable material which serves to both prevent slippage or sliding of the sheet material and to seal the sheet material structural frame interface, thereby protecting the container contents from the elements.
An easily removed cap is mounted to the structural frame to keep the sheet material within the structural frame and to serve as a roof attachment point.
The transparent side walled container of the present invention is capable of free standing use, such as, for example, an intermodal transport container or air cargo container, or it may be mounted to a vehicle frame for use in, for example, a semi-trailer or rail box car.
One advantage of the present invention is the ability to allow easy and efficient visual access to security personnel to assist them in determining whether the container contents have been altered since their original loading or pose some other security risk.
Another advantage of the present invention is the ability to easily and cost efficiently replace a damaged side panel with out the need for specialized tools.
Still another advantage of the present invention is the reduction of wind resistance (resulting in greater fuel economy) through the reduction of required numbers of bolts, nuts, rivets and other fasteners previously used to attach a side panel to a structural element.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.